This invention relates to an electronic blackboard, especially to an eraser used for it and more particularly the present invention provides an eraser which has a variable erasing area.
An electronic blackboard is a device developed for displaying a signal, written by hand on an input board using a hand-held input instrument, on an electronic display unit. Such a device has been proposed for use in a conference system by interconnecting isolated conference rooms using telephone lines etc. Such a system is beginning to be put into actual use under trade names "Gemini 100" by AT&T or "OA Board" by Fujitsu Ltd. etc.
The electronic blackboard detects the positional coordinates of the hand-held input instrument, such as chalk, pencil, felt pen or some special input instrument, when it contacts the surface of the input board (such an input board is sometimes called as digitizer). The coordinates of the touched points are detected and stored in a memory or transmitted to a display unit, and the trace of touched points (figures) are displayed on the display unit.
Electronic blackboard systems can be roughly classified into two kinds by the method of how detection of the coordinates of touched points occurs. One is a pressure sensing type, which detects the contact point of the hand-held instrument on the input board by using a pressure sensitive board. The other is an electro magnetic types which can be further classified into electric and magnetic type, according to whether the coordinate detection is performed by electric or magnetic coupling of the detector to the electronic blackboard or input board.
The electromagntic detection type can be further classified into two types. One is an active board and passive pen type system, that is a position signal is generated by the the input board (active board) and detected by the pen or eraser (passive pen). The other one is a passive board and active pen type system, that is the pen or eraser generates a signal (active pen) detected by the input board (passive board).
The present invention is related to an eraser used for erasing a figure written on the surface of the input board, and blanking the locations in a memory corresponding to the erased part of the figure, to erase the corresponding part of the figure displayed on display unit. It is especially intended to provide a new eraser, whose erasing area can be varied for user convenience to erase a large or small area of the displayed figure.
The following explanation will be given with respect to a magnetic type electronic blackboard, and especially with respect to an active board and passive pen type system. However the explanation is essentially the same for the other types of systems, and can be extended to any type of electronic blackboards except the method of detecting the positional coordinate of the input instrument or eraser on the surface of the input board.
The essential parts of a magnetic type electronic blackboard are shown in FIG. 1. In a blackboard (tabulator of figures written on an input board) 1 is installed a number of coils arranged in X and Y directions with the interval between the coils depending upon the desired resolution. The coils are fabricated usually by printed circuit technology and are called X-coils 2 and Y-coils 3 respectively, according to their direction of arrangement as shown in FIG. 1. These x-coils 2 and Y-coils 3 are excited using electric current and generate magnetic fields at specified intervals in the order of the X and Y directions. When a figure or letter 6 is written on the board 1 (it is not necessarily black in color) using a felt pen 5, a detection coil 4 installed in the felt pen 5, detects the magnetic field emanation from the surface of the board. From the timing or phase of the magnetic field detected by the coil 4, the positional coordinate of the felt pen 5 on the board 1 is detected and the FIG. 6' written on the board 1, can be shown on a display unit 7.
An eraser for such a system is similar to the input pen. When the figure on the input board is erased by hand with an eraser having a felt point for example, a detection coil installed in the eraser detects the magnetic field produced by the input board. The positional coordinates of the eraser are detected in the same way as those of the input pen, and the memory locations corresponding to the trace of contacted points by the eraser on the surface of the input board (that is the part of the figure erased by the eraser) are blanked or cleared. Thus the corresponding part of figure on the display unit is erased.
When using the prior art electronic blackboard, the person who uses the blackboard eraser experiences inconvenience when erasing figures because the point of the eraser is fixed to an appropriate size or area, and if the person wants to erase a large area, he has to use the eraser many times. However, if he wants to erase a fine or sharp figure, a wrong part can be erased by the improperly large eraser. And if the user tries to erase a fine figure by leaning the eraser on its edge similar to when using a general blackboard eraser, errors occur in positional detection and the displayed figure can be deleted incorrectly.
Simple method of responding this problem is provide two erasers, large and small. However this method results in an increased number of components and an increased in cost. The inconvenience caused by the need of changing the eraser in hand is not overcome.